Automatic valve timing device



May 1, 1934- E. w. MITCHEL. 1,957,181

AUTOMATIC VALVE IIMING DEVICE Filed Feb. 27, 1932 ATTORNEYS` PatentedMay l, 1934 UNITED STATES PATENT FFECE AUToMATIo VALVE TIMrNc DEVICEEdward W. Mitchel, Detroit, Mich. Application February 27, 1932, serial10,595,532

4 Claims.

This invention relates to internal combustion engine construction, andmore particularly to such engines having cam-operated intake and exhaustvalves. The invention has for one of its 5 objects provision of meansfor automatically changing the timing of the opening and closing of theintake and exhaust valves of such an engine in accordance withvariations in the speed at which it is running.

As is well known, when a gasoline engine is running at high speed, thevalves require more lead than when the engine is running at low speed,and in fact it is common to open the eX- haust valves of a high speedengine twenty or thirty degrees before the pistons reach the bottom oftheir power strokes. It is not possible in commercially practicalconstructions as now made, however, to provide as little lead as isrequired fer maximum einciency at low speed, else at higher speeds theback pressure would be so great as to cause undue vibration, knockingand stalling. I have found such back pressure caused by insuicient valvelead to be one of the most common causes of engine vibration. On theother hand, if adequate lead for high speed operation is provided, thepremature opening of the valves at low speeds causes such loss of poweras to very deleteriously affect the engines performance. It is the usualpractice, in order to minimize these difliculties, to compromise as tovalve settings, and to so arrange their timing that the lead is properat some intermediate speed; so that even though it is thereforenecessarily too little at higher speeds and too great at lesser speeds,the engines performance will be affected as little as possible. Theineiiciency thus introduced does, however, detract from the enginesperformance, and that to an extent so serious that marked improvement iniiexibility, smoothness and power is obtainable by remedying theseundesirable conditions, and providing proper valve timing at all speeds.This my invention is aimed to and does accomplish as its most importantobject.

By means of my improved automatic valve timing construction I am enabledto maintain the proper valve lead at all times, and thus to greatlyimprove the performance of -a gasoline engine with which it isassociated, at both low and high 50 speeds, reducing vibration at allspeeds and adding considerably to the maximum speed of the engine, sinceback pressure, due to insuicient valve lead is not permitted to buildup.

It is a further object of this invention to provide 55 such an automaticvalve timing device which is so (Cl. (i4-90.5)

simple, rugged, and inexpensive in construction as to be practical forinstallation as standard equipment upon gasoline motors produced inquantities, and, barring material iiaws, invariably capable of lastingthe full life of the engine without requiring attention or adjustment.

Other objects and advantages will be apparent from the followingdescription, wherein reference is made to the accompanying drawingillustrating a preferred embodiment of my invention, and wherein similarreference numerals designate similar parts throughout the several views.

In the drawing:

Figure l is an elevational view showing in plan the arrangement of partsemployed in one form of my invention.

Figure 2 is a vertical sectional view taken substantially on the line 22 of Figure 1 and looking in the direction of the arrows there shown.

Figure 3 is an elevational view taken looking at the opposite side ofthe assembly from Figure 1 with the closure plate partly broken away andshowing in dotted lines the fly weights in their innermost positioning.

Figure 4 is a similar elevational view, with the closure plate removed,showing in dotted lines the fly weights in their outermost positioning,resulting from suiciently rapid rotation of the unit.

Figure 5 is a vertical sectional view taken substantially on the line5-5 of Figure 1 and looking in the direction of the arrows there shown.

Figure 6 is a sectional elevational view taken 90 substantially on theline 6 6 of Figure 2 and looking in the direction ofthe arrows, bringingout the construction and arrangement of the inner faces of the flyweights and parts carried thereby, and showing the weights in theiroutwardly moved positioning, and f Figures '7 and 8 are detailedperspective views of the cam-actuating stud members I employ forrotating the hub relatively to the gear.

Referring now to the drawing: Reference character 20 designates the camshaft gear of an in-` ternal combustion engine, generally designated 50,This gear, in ordinary engine constructions, is rigidly secured to thecam shaft and positively driven, usually at fractional crank shaftspeed, by a driving gear on the crank shaft. In such a construction itis possible to Vary the timing of all the valves simultaneously only byturning one of these gears a few teeth relatively to the other, or oneof the shafts relatively to the gears In my improved construction Iprovide a hub 21 for the gear 20, which is loose relatively thereto, sothat the hub and the toothed portion of the gear may turn relatively toeach other. The gear is of ring form, and interiorly provided with aflange 22, as shown in Figures 2 and 5. Secured to the ilange. as byscrews 23, are the annular plates 24-25, the aligned axial apertures26-27 of which rotatably carry the hub 2l. The hub 2l is keyed orotherwise ilxed to the cam shaft, and integrally carries the fla-ngeplate 28, which radially projects and is slidable between the plates24-25. The hub 21 and flange 28 are thus free to turn relatively to thegear and plates 24-25.

Cam slots 29-30 are formed in the flange 28, their substantial contourbeing best shown in Figures 3 and 4, and slidable therein are stud-likefollowers 3l and 32, which extend through guide slots 33 in the plate25. The slots 29, 30, and 33 are so contoured as to enablecircumferential movement of the hub relatively to the gear when thestuds 3l and 32 are simultaneously moved outwardly or inwardly in theslots 33. When the studs are moved outwardly, they move the hub 21 andthus the cam shaft in the proper direction to advance-the lead, byturning the plate 28, and thus the hub, relatively to the positivelydriven ring gear portion 20, due to the inclination of the cam slots.

In order to provide for gradual automatic outward movement of the camstuds concurrently with increasing engine speed, and for similar inwardmovement thereof ccncomitantly with decrease of engine speed, I providethe governing ily weights 34-35, which are mutually outwardly movableunder increasing centrifugal force caused by mounting engine speeds butnormally indrawn by tensile springs, as 36-37-56--5'7-58. All of thesewith the exception of the spring 58 act in tension, their ends beingsecured directly to the fly weights, in apertures in which they are alsopartially housed, as clearly shown in the drawing. Companion spring 58is trapped upon the overlapping portions of the hooked supporting stopsrigidly carried byl and projecting inwardly from the ily weights in suchmanner that the spring 58 acts to supplement the resistance of theremaining springs to outward movement of the weights when the latterapproach the outer limit of their travel, while the hooked supportsadditionally provide, in combination with the spring 58, a positive stoplimiting outward movement of the weights. The ily weights may bedirectly connected to the studs, as by extending the threaded endportions 38-39 of the studs for that purpose, and forming suitableapertures 40 in the ily weights to receive them. Securing nuts 4l arescrewed upon the threaded end portions 38 and 39 of the studs, and setflush if desired in counterbored portions 42 of the stud apertures 40.To insure smooth sliding movement of the fly weights relatively to eachother, I preferably secure to each an extended slotted slide bar (43-44). Slots 45 and 46 in the bars serve as slideways in which theflattened central portions 32 of the studs 32 slidably lit, as shown inFigures 1, 5 and 6. The bars 43-44 additionally control the slidingmovements of the weights by engaging in slots or kerfs 47-48, one formedin each ily weight opposed to that carrying the slide bar which engagestherein, to enable their engagement in the slideways -46. The centralportions 32 of the studs 32 are made longer than the similar portions 3lof the studs 31, so that in the case of the studs 32, these portionsproject a suitable distance from the plate 25 for engagement in theslots, as shown in Figures 5, 7 and 8.

The resistance of the springs 36-37 is of course so proportioned to theweights 34-35, and to the cam slots, as well as to the extent of therelative movement desired to be imparted to the hub 2l, that upon anyincrease of engine speed, the extent of outward movement of the lyweights will be so proportioned relatively to such increase as toadvance the hub relatively to the driven portion of the gear, and thusthe lead of the valves, to an extent adapted to maintain such lead inproper relation to the engine speed. It will be seen that speedvariations will result in whatever outward or inward movement of theweights is necessary to balance the centrifugal and centripetal forcesacting upon them. These movements are translated, by the describedmechanism, into relative turning movement 0f the cam-shaft with respectto its driving gear, in the proper direction and to the proper extent tomaintain the valve lead at its most elcient setting.

The actual quantity and design values of such factors as weights, springresistances, cam slot development, etc. are of course dependent upon thecharacteristics of the engine with which the device is to be used, andthose skilled in the art will be readily capable of calculating thesefactors for any given case, now that I have disclosed a mechanicalmethod by means of which the desired result may be effected.

While the operation of the device is doubtless clear from the foregoingdescription, it might brieily be summarized as follows: When the motoris turning over slowly, centrifugal force is insufficient to throw theweights 34-35 outwardly to an appreciable extent against the tension ofthe springs 36-37-56-57-58, and their centripetal pull maintains theweights in indrawn position, and thus holds the cam-actuating studs 3land 32 at the inner ends of the slots 33. The inclination of the camslots 29 and 30 is such that the stud heads, upon moving outwardlytherein, rotate the flange 28 and thus the hub 21 in the properdirection, and to the proper extent, in accordance with and dependentupon the instant speed of the engine, to compensatingly advance thevalve lead to maintain the same at the point of maximum efficiency,while likewise upon slowing of the engine the stud heads, drawn inwardlyby the springs 36-37-56-57-58, retard the hub 21 and thus the cam shaftrelatively to the gear in like manner to decrease the valve lead. Thedirections of rotation and of movement of the parts upon acceleration ofthe motor are indicated in this particular case by arrows 50, 51, and 52in Figure 1.

It will be seen that the movement imparted by the studs is irreversible,however, and that no matter what changing resistance to rotation the camshaft may offer, no thrust thus imparted can vary the spacing of the ilyweights which is for all practical purposes entirely controlled bycentrifugal force and the opposing spring tension.

The preferred embodiment of my invention herein disclosed andillustrated has been chosen as illustrative of the most effective andcompact organizations of basically similar or equivalent parts for theaccomplishment of the purposes herein stated, but I desire it to beunderstood that within the fair field and spirit of the language of thesubjoined claims structural variations from what is herein illustratedmay be indulged` in without departure from the intended eld of thisdisclosure.

What I claim is:

1. Means for controlling the cam shaft of a poppet valve engine,comprising a gear and hub rotatable relatively to one another and havingoverlapping portions with intersecting cooperating cam slots therein,said slots having portions angularly disposed relatively to each other,a pin extending through and slidable in both slots and adapted whenmoved therein to turn the hub relatively to the gear, the relativeangularity of the slots being small, so that the pin can not be moved inthe slots by torque applied to either the hub or gear member, and a flyWeight connected to the pin to move the same and so change the relativepositioning of gear and hub in response to speed variations.

2. Means for automatically controlling in response to engine speed thevalve timing of an internal combustion engine incorporating intake andexhaust valves and a valve actuating shaft, comprising a hub adapted tobe affixed to such a shaft, an annular gear carried by the hub androtatable relatively thereto, means for positively driving the hub bythe gear at any of various relative angular positions, comprising alimitedly radially movable fly-weight ca ried by the gear, and combineddriving and shifting means connecting the weight and hub for bothcontinuously turning the hub and for shifting the hub relatively to thegear upon radial movement of the ily-weight caused by variation of itsspeed of revolution, including a plurality of cam portions arranged atsmall angles relatively to each other, and common actuating meanstherefor connected to the ily-weight, said Weight being thereby notradially shiftable by torque transmitted through the hub.

3. Means operatively connectible with the valve actuating shaft of aninternal combustion engine whereby timing of the opening and closing ofthe valves may be automatically regulated, comprising a pair ofoverlapping and relatively movable driving and driven members having aplurality of pairs of partly registering cam slots therein withrelatively angular portions, a driving pin extending through each pairof slots and movable therein to turn the driving and driven membersrelatively to each other, the slots of said pairs being arranged atsmall angles relatively to the paths of pin movement, whereby neitherthe driving nor driven member can be moved relatively to the other byforce transmitted through the pins, and means including a fly-weightresponsive to speed variances for actuating said driving pinsresponsively to engine speed variances, and means resiliently in-drawingthe last mentioned means.

4. Means for controlling the valve-timing of an internal combustionengine incorporating intake and exhaust valves and a valve-actuatingshaft, comprising a driving member adapted to be carried by such a shaftin lost motion connection therewith, a driven member adapted to berigidly aixed to the shaft, said driving and driven members havingpartly registering relatively angular oam slots therein, a driving pinextending through said slots and movable theree in to change therelative angularity of the driving and driven members, and meansincluding a fly-weight for moving the pin in response to speed changes,the slots being arranged at a small angle relatively to the paths of pinmovement, whereby the pin is movable by the ilyweight but not by torqueapplied through a slotted member.

EDWARD W. MITCHEL.

